Self-propelled wheelchair

ABSTRACT

A self-powered wheelchair with four ground engaging wheels, the two rear wheels being mounted on a rear axle that is pivoted about a fore and aft axis at its mid-point for limited tilting in a vertical, transverse plane, one of the front wheels being an idler at one side of the chair, and the other front wheel being part of a power unit at the opposite side of the chair. The power unit is steerable about a vertical axis by turning a steering shaft that rises upwardly and turns rearwardly to present a tiller arm, such tiller arm having a control box at its upper end that presents a vertical palm engageable handle for turning the tiller, and a vertically depressible thumb engageable speed selector rod for governing the speed of the chair. There is also a brake mechanism associated with the rear wheels of which a part tilts with the rear axle and mounts brake shoes to apply desired braking force regardless of the degree of axle tilt.

nited States Patent 1191 Moon [451 Feb. 26, 1974 SELF-PROPELLEDWHEELCHAIR I Primary Examiner-Even C. Blunk 75 lnventor: Robert W. MoonShore od, W Assistant Examiner "Johnny Cherry 1 W ls Attorney, Agent, orFirm-Arthur H. Seidel [73] Assignee: Lakeside Manufacturing Inc.,

Milwaukee, Wis. 57] ABSTRACT Filed: 1972 A self-powered wheelchair withfour ground engaging [21] APP] 281,081 wheels, the two rear wheels beingmounted on a rear axle that 1s pivoted about a fore and aft ax1s at itsm1dpoint for limited tilting in a vertical, transverse plane, [52] Us (1180/13 180/26 180/65 one of the front wheels being an idler at one sideof 280/111 the chair, and the other front wheel being part of a [51 h t.Cl B62d 61/00 power unit at the opposite Side f the chain The [58] heldof Search" 180/13, 26 power unit is steerable about a vertical axis byturning 180/DlG. 3; 188/2 F; 280/111 a steering shaft that risesupwardly and turns rearwardly to present a tiller arm, such tiller armhaving a [56] References C'ted control box at its upper end thatpresents a vertical UNITED STATES PATENTS palm engageable handle forturning the tiller, and a 2,838,124 6/1958 Cramer 280/111 x verticallydepressible thumb engageable Speed Selector 2,392,506 6/1959 Slater180/26 R rod for governing the speed of the chair. There is also3,023,825 3/1962 Rabjohn.... 180/15 a brake mechanism associated withthe rear wheels of 3,179,199 4/1965 o a 180/65 R which a part tilts withthe rear axle and mounts brake 3,387,681 6/1968 J n 1803 shoes to applydesired braking force regardless of the 3,605,929 9/1971 Rolland 180/26R degree of axle tilt 3,664,450 5/1972 Udden et al. l80/65 R I 10Claims, 14 Drawing Figures 53 SA 1 l 5 5- I V 80 7 a v a a 4' T7 4 6:6 6I 1 v 1 3e 5 1 4 J5 T 4 In H a a i y 8 I I I z 57 44 H a i 1 37'': E5 I7 Z5 1 4-0 3 I!" D l K 42' "1. )5 3 1" I"; 74 1, I 1/ 11, H I, h 4n 1'Iii" i731 4/1, "I" III 1 1. ,0 27 4/ 1,

SELF-PROPELLED WHEELCHAIR BACKGROUND OF THE INVENTION a. Field of theInvention The present invention pertains to motorized wheelchairs forelderly people, the incapacitated and infirm, patients, and the like. 1

b. Description of the Prior Art Mechanized wheelchairs with electricmotor drives have been known, and have taken a variety of differingdesign forms, but they have not found widespread usage among those whocould benefit from their use. Some of the earlier designs retained thebasic design of hand driven wheelchairs that are characterized by alarge diameter wheel at each side which extends upward above chair seatheight, and which may be grasped by the user for propelling and steeringthe chain. One such form is shown in U.S. 'Pat. No. 2,448,992 wherein adetachable power unit with a single ground engaging wheel is attached tothe rear of a wheelchair. The power unit contains a motor and battery,and a control arm extends forward from the power unit alongside thechair. This design creates a five wheel vehicle, makes for a very largecumbersome device, and adds expense directly to the full expense of anordinary chair.

A somewhat similar approach, of preserving large wheels and the basicdesign of a manual chair, is disclosed in U.S. Pat. No. 2,635,703.There, two large wheels are retained at the rear, and a single wheel ofa motor driven unit is located at the front. A three wheel deviceresults which is less stable than conventional four wheel chairs, andifthe userfs weight shifts forward a rocking can occur about the single,front wheel. Tilting, to the point of upsetting the chair, can occur inextreme conditions of weight shift. Although a three wheel vehicle hasthe inherent disadvantage of decreased stability this type of design hasbeen carried over into a number of chairs, as evidenced by U.S. Pat.Nos. 2,482,203 and 3,213,957.

A three wheel device ensures that each wheel engages the ground at alltimes, and where one of the wheels provides power for locomotion andsteering this is quite essential. In a four wheel vehicle, if one wheeldrives and steers, and loses engagement with the ground, then control islost. This cannot be tolerated, for a wheelchair carrying an invalid,aged person, or patient must feel secure to the user at all times.

At least two designs have been suggested for preserving the desirablestability characteristic of a four wheel chair, while still having asingle driving wheel engaging the ground. In U.S. Pat. No. 3,023,825 thedriving wheel is added as a fifth wheel directly in front ofa forwardwheel at the front of the chair. A spring biases the driving wheeldownward, so that it engages the ground even though the associated frontwheel might leave the terrain because of unevenness or some similarreason. In related U.S. Pat. No. 3,387,681 the associated front wheel iseliminated, and a spring suspension forthe driving-steering wheel keepsthe wheel in contact with the ground at all times. This laterconstruction has had commercial application for several years.

SUMMARY OF THE INVENTION wheels are tied together on a common axle thattilts about a transverse pivot axis, to result in an effective threepoint type engagement that maintains a powersteering wheel in groundengaging contact, but which exhibits the stability of four wheelvehicles. The invention may further include a brake mechanism for thepivotable axis that has a brake rod mounting brake shoes alongside theaxle supported wheels that pivots with the axle, and which also hasmanually operable portions on the chair proper which have a lost motionconnection with the brake rod. In its fullest form, the invention alsohas improved steering and speed control.

To combine both the stability of four wheel construction and the groundhugging of three wheel construction into a wheelchair that is designedspecifically for motor driven operation, in which there is a singlepower-driven wheel that should be kept in ground engagement at alltimes, regardless of any uneveness of terrain, the present inventionmakes use of an axle pivoted near its mid-point about a four and aftaxis. This type of wheel suspension, in itself,'is not new as evidencedby U.S. Pat. Nos. 2,79l,044 and 2,5l0,424, wherein cart beds have oneset of wheels suspended in such manner, and U.S. Pat. No. 3,605,929wherein a three wheel golf cart has two rear wheels suspended on apivoted axle frame. U.S. Pat. No. 3,159,229 makes a related showing of avehicle chassis divided into component parts that are connected by auniversal joint.

The present invention, however, makes a pivoted axle constructionfeasible for a wheelchair by introducing several novel concepts. Thepivotal motion is limited by stop abutments extending over the axlewhich are an integral part of the framework of an undercarriage for thechair proper. In preferred form, the abutments can serve the doublefuntion of a rack for an energy cell and a storage box, and by limitingthe degree of axle pivot attainable the user of the chair will feelsecure and have confidence in the use of his chair regardless ofinfirmities he may be subjected to such as age, post-operativedebilities, or other physical impairments.

Positive braking is provided for the rear wheels by a unique mounting ofthe braking shoes that are brought to bear against the wheels. The shoesare mounted to move with the wheels as any axle pivot occurs, so thatthe wheels and shoes remain aligned at all times. A lost connection isprovided between the support of the shoes and the manual controls of thebrake system, so that the manual portion of the brake mechanism remainin fixed position regardless of axle position. Hence, there will not beany inconvenience to the user of the wheelchair. Further, the lostmotion connection does not lose any appreciable braking forcestransmitted through it, wherefore braking action is not diminished byany axle pivot that may occur.

Another aspect of the invention is improved steering. A steering handleis provided which is grasped by the palm and fingers for turning thevehicle. A vertically depressible rod concentric with, and protrudingabove the steering handle controls speed, and the thumb motion is aseparate muscular movement distinct from that of the steering action.lnfirm people can master this dual, muscularly separate control system,so as to operate the wheelchair with confidence and without confusion.

Other objectives of the invention include comfort for the user of awheelchair; reductions in costs to enable a more widespread use ofmotorized wheelchairs; location of all four wheels within theextremities of the framework serving as an undercarriage for the chairproper; ease of steering and handling; reversibility of positions of thefront wheels to have either left hand or right hand side steering; easeof entry and exit from a chair; sufficient collapsibility for shipping;housing a drive motor and its power consuming electrical controlcomponents within a single hood; easily operable speed control andforward and reverse operation of a wheelchair; and maintenance of thecomposite center of gravity of a wheelchair, its power supply, and of auser in normal position well within the outline of the points of groundengaging contact of the chair.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in perspective of awheelchair embodying the present invention,

FIG. 2 is a left side view in elevation of the wheelchair with someparts drawn in phantom and with a luggage box having a portion thereofbroken away and in section,

FIG. 3 is a top view of an undercarriage portion of the wheelchair takenthrough the plane 3-3 indicated in FIG. 2,

FIG. 4 is a view in section of a portion of the undercarriage of thewheelchair taken through the plane 4-4 indicated in FIG. 2 whichintersects the axle ofthe rear wheels of the wheelchair,

FIG. 5 is a fragmentary view on an enlarged scale of the right hand rearportion of the wheelchair showing a brake mechanism in conjunction withthe rear wheels,

FIG. 6 is a fragmentary view of the backrest of the chair taken throughthe plane 6-6 indicated in FIG. 1,

FIG. 7 is a fragmentary plan view in section with parts broken awaywhich is taken over the front wheels through the plane 7-7 indicated inFIG. 2,

FIG. 8 is a fragmentary view of a steering column forming a part of thewheelchair which is taken through the plane 77 and which is on anenlarged scale as contrasted to the drawing of FIG. 7,

FIG. 9 is a view in vertical section of a control box and operatinghandle for the wheelchair,

FIG. 10 is a top view of the mechanism of FIG. 9 taken through the plane10-10 indicated in FIG. 9,

FIG. 11 is a view in cross section of the mechanism of FIG. 9 takenthrough the plane 11-11 indicated in FIG. 9,

FIG. 12 is an enlarged view of the bottom portion of a power unitforming a part of the wheelchair with a cover that normally shrouds thepower unit removed to expose the interior;

FIG. 13 is a view of the power unit shown in FIG. 12 as seen from theopposite side thereof, and

FIG. 14 is a front view ofthe power unit of FIGS. 12 and 13.

DESCRIPTION OF THE PREFERRED EMBODIMENT The perspective view of FIG. 1shows a wheelchair having a cushion seat 1 supported on a pair of foreand aft extending side frames 2. Rising upward from each side frame 2are fore and aft vertical frame members 3 and 4 that support an arm rest5. Between the two vertical aft frame members 4 there is supported apivoted backrest 6 that is shown in an upright position in FIG. 1, and alowered, or depressed position in FIG. 2. As shown in FIG. 6, a pair ofspring biased pins 7 mounted in the aft frame members 4 enter brackets6' fastened to the sides of the backrest 6 to hold it in an uprightposition. The purpose of having the backrest 6 fold downward, as shownin FIG. 2, is to facilitate storage, shipment in a carton, or transportin vehicles such as station wagons having limited height openingsthrough which the wheelchair may be inserted.

THE UNDERCARRIAGE FRAMEWORK To support the chair proper, make up of theseat 1 and backrest 6, two front legs 8 and two rear legs 9 extenddownward as continuations of the vertical side frames '3 and 4. A pairof longitudinal, base forming joists 10 located one at each side of thewheelchair are parallel to the ground and extend between the front chairlegs 8 and the rear chair legs 9. A pair oftransversely extending joists11, also parallel to the ground, extend transverse of the wheelchairwith one joist 11 connecting between the lower ends of the front chairlegs 8 and the other joist 1l connecting between the lower ends of therear chair legs 9. The resulting quadralateral base framework is shownin FIG. 3.

A pair of fore and aft, or longitudinally extending, rack rails 12 arefastened at their forward ends upon the front transverse joist l1 and attheir after ends on the rear transverse joist 11. The rack rails 12 arespaced equal distances on opposite sides of the fore and aft center lineof the wheelchair, and they are L-shaped in cross section, as indicatedin FIG. 4 to present a support for both a battery case 13 and a luggagebox 14. The luggage box 14 is directly behind the battery case 13 toserve as a convenient receptacle for items of the person confined to thewheelchair. Only a minor fraction of the luggage box 14 is shown in FIG.3, so as to reveal the construction of portions of the undercarriagethat are directly beneath the luggage box 14.

The battery case 13 is of a size to accommodate an ordinary storagecell, and the location of the battery case 13 is seen to be directlybeneath the center of the chair cushion 1, so as to locate the center ofgravity of this relatively heavy item at, or near, the geometric center.The battery case 13 is also in substantial vertical alignment with theintended position of the center of gravity ofa person within thewheelchair, so as to en hance the stability of the structure. To holdthe battery case 13 firmly in place, a chip 15 may be used as shown inFIGS. 3 and 4.

THE REAR WHEEL SUPPORT Referring now particularly to FIGS. 3 and 4, atransverse strap 16 extends between the two rack rails 12 some distanceforward of the rear transverse joist 11. On the underside of thetransverse strap 16 is secured a bearing 17, and a similar bearing 18 issecured to the underside of the rear transverse joist 11. The centerlines of the two bearings 17, 18 are aligned with one another along thelongitudinal center line of the wheelchair. A short pivot shaft 19 ismounted in the bearings 17, 18 to form a pivot therewith, and tightlysecured upon the pivot shaft 19 at its mid-point is a rear axle 20. Therear axle 20 is a box shaped tubular member, and at each end of thischannel shaped member is secured an upwardly rising offset 21. A sideview of an offset 21 is particularly well shown in FIG. 5, and the upperend As is particularly illustrated in FIG. 4, the pivotal.

mounting of the rear axle at its mid-point on the pivot shaft 19 permitseach of the rear wheels 23 to rise and fall with respect to theundercarriage and the remainder of the wheelchair. This permits somedeviation of the axle 20 from the wheelchair proper, so that when uneventerrain is encountered the rear wheels 23 can move to a limited degreethat permits the chair portion of the wheelchair to remain stable in anearly horizontal position, thus giving a more comfortable ride and asecure feeling to the user of the wheelchair.

The pivotal movement of the rear axle 20, about the pivot comprising theshaft 19 and the bearings 17, 18 is limited. This limitation arises froma closed spacing of the top of the rear axle 20 from the underside ofeach of the rack rails 12. When the axle 20 is aligned with theremainder of the wheelchair, as shown in FIG. 4, there is a small gap 24between the top of the axle 20 and each of the rack rails 12. Thus, thebottom faces of the rack rails 12 function as motion limiting abutmentsfor the axle 20. As a result, there is some limited pivotal motion ofthe axle 20 in response to uneven terrain which produces a smoother,gentler ride, but it is limited so that a person who is in thewheelchair will neither feel an unsteady chair beneath him, nor willdangerous tilting motion of the entire chair occur which might upset thechair or make the user uneasy.

THE BRAKE MECHANISM Referring particularly to FIG. 5, a substantiallyhorizontal link 25 is pivoted at its rear end to the bottom of thevertical axle offset 21, and this structure is duplicated at theopposite end of the rear axle 20. Extending between the forward ends ofthe two links 25 is a rod shaped brake shaft 26. It is seen that therear, pivoted ends of each of the links 25 is disposed a distancedownward from the center of rotation of the rear wheels 23, asrepresented by the stub shafts 22, so that when the links 25 are raisedtheir forward ends will carry the brake shaft 26 toward the faces of therear wheels 23.

Mounted on the outer ends of the brake shaft 26 is a pair of brake shoes27, each shoe 27 being in direct facing relation to the periphery of anassociated rear wheel 23, as shown in FIG. 3. Hence, by a swingingmotion of the links 25 and the brake shaft 26 the brake shoes 27 aremoved into and out of engagement with the faces of the wheels 23. Thus,braking force can either be applied or released, and since the links 25and brake rod 26 are carried by the axle 20 the brake shoes 27 areconstantly in alignment with the wheels 23.

To operate the brake shoes 27 there is provided a manual brake handle28, clearly shown in FIG. 5, that rises upwardly alongside the chaircushion l. The brake handle 28 extends through an appropriate opening inthe right hand side frame 2 and is notched to engage a catch 29 on theunderside of the frame 2. A coil spring 30 biases the brake handle 28upward, and an upward motion of the handle 28 will function to releasethe brake shoes 27 from the rear wheels 23.

The bottom end of the brake handle 28 is pivotally connected with abrake lever 31 which is made up of several parts. These parts are bestseen in FIGS. 3 and 5. The brake lever 31 has a pivoted rod 32 extendingbetween and beneath the rack rails 12. One end of the rod 32 is securedto a strut 33 that joins with the lower end of the brake handle 28, sothat an up and down motion of the brake handle 28 will result in a pivotof the rod 32. At the mid-point of rod 32 there is integrally fastened,as by welding, a connection hook 34 which, as seen in FIG. 5, partiallyencircles the brake shaft 26. The connection of the hook 34 with thebrake shaft 26 is a lost motion connection, in that the brake shaft 26is free to pivot in a teeter-totter like motion within the hook 34without losing engagement between the parts. Any pivot of the brakeshaft 26 will be due to the corresponding pivot of the rear axle 20,which is translated through the link 25 to the brake shaft 26, asdescribed above.

It is readily seen that when the brake handle 28 is depressed theconnection hook 34, which is fast upon the rod 32, will rise, and inturn lift the shaft 26 upward to bring the brake shoes 27 intoengagement with the rear wheels 23. An upward motion of the brake handle28 will cause a reverse of this operation in which the brake rod 26falls and the links 25 controlling the radius of motion move the brakeshoes 27 away from the faces of the wheels 23.

A particular feature of the brake mechanism is the development ofpositive braking force applied to both rear wheels 23 regardless of theangle of pivot of the rear axle 20. As has been indicated, the brakeshoes 27 are mounted so that they move with the pivoting motion of therear wheels 23 to maintain proper alignment of these portions of theapparatus. On the other hand, the brake actuating mechanism constitutingthe brake handle 28 and the brake lever 31 are maintained in a fixedrelation with the chair proper, so that at all times the brake handle 28is in a position that remains constant insofar as the operator of thewheelchair is concerned.

THE FRONT FRAMEWORK Referring now particularly to FIGS. 1 and 2, thereextends forward from each side of the chair a cantilevered, front wheelsupporting frame 35. Each frame 35 is comprised of an extension 36 of aside frame 2, a forwardly and obliquely downward extending strut 37, anda lower horizontal brace 38 reaching between the lower end of the strut37 and a front chair leg 8. Between the braces 38 there extends areenforcing cross bar 39. Telescoped within the struts 37 are adjustablelegs 40 which carry pivoted foot rests 41 at their lower ends. Byadjusting the legs 40 within the struts 37 the foot rests 41 can beraised and lowered to suit the need of the occupant of the wheelchair.

An idler type front wheel 42 is located on the right hand side of thewheelchair and is borne by a forked castor 43. The castor 43 is carriedby a bearing housing 44, which has an L-shaped mounting bracket 45, asparticularly shown in FIG. 7. The bracket 45 is secured to the righthand brace 38 and the cross bar 39 by a pair of mounting bolts 46, 47.The idler wheel 42 functions to support the front, right corner of thewheelchair, and it freely pivots about its vertical axis in tandem witha front power wheel to be described.

A seoond L-shaped wheel mounting bracket 48, which is shown in FIGS. 7,12 and 13, is mounted by a set of bolts 49 and 50 to the left hand endof the cross bar 39 and the left brace 38. The size and shape of the twomounting brackets 45, 48 is the same, and the position of the bolt holesfor the mounting bolts 46, 47, 49 and 50 are such that the brackets 45and 48 can readily be interchanged'in position. This allows for mountingthe ground engaging idler wheel 42 on either side of the wheelchair, andsimilarly the power unit to be described can also be mounted on eitherthe right or left hand side of the wheelchair, to suit the needs ordesires of the user of the chair.

THE STEERABLE POWER UNIT Referring now to FIGS. 12 and 13, a circular,cylindrical bearing housing 51 that is like the housing 44 is secured onthe bracket 48. The housing 51 has an internal bearing 59 that receivesthe lower end ofa vertical, tubular shaft 52. There is a steerable powerunit 53, shown on an enlarged scale in FIGS. 12, 13 and 14, having astub shaft 54 inserted tightly into the bottom of the tubular shaft 52,and the stub shaft 54 is hollow to accommodate control wires 55 thatextend through the length of the tubular shaft 52.

On the bottom of the stub shaft 54 is a castor 56 presenting a pair ofspaced, downwardly extending castor legs 57 that are bridged at theirtop by a web 58. Rotatably mounted between the lower ends of the castorlegs 57 is a rubber tired, ground engaging, drive wheel 60 that has alarge gear wheel 61 attached to one side thereof in concentric relationwith the axis of rotation.

Secured to the top rear of the castor legs 57 is a transverselyextending motor bracket 62 that mounts an electric motor 63 powered bythe energy cell within the battery box 13. As seen in FIG. 12, the motorshaft has a small diameter, toothed gear wheel 64. A toothed belt 65that is driven by the wheel 64 travels around a large diameter, toothed,reduction gear wheel 66. The wheel 66 is mounted on and drives an idlershaft 67 that is borne between the castor legs 57 at a position abovethe drive wheel 60. Secured to the idler shaft 67, and located betweenthe two castor legs 57, is a pinion gear 68 which drives a chain 69 inmesh with the large diameter gear 61 fastened on the side of the drivewheel 60.

A keeper pinion 70 is rockably mounted on an arm 71 depending from theidler shaft 67, and a bias spring 72 urges the keeper pinion 70 intomesh with the chain 69 to keep the chain 69 taut at all times. Thisensures positive, mating engagement between the chain 69 and the gearteeth of the pinion 68 and the large gear 61, and it also functions toreduce lost motion between forward and reverse operation of thewheelchair.

A highly heat conductive plate 73, preferably of aluminum or like heatconductive metal, is mounted transversely across the castor legs 57 onthe front side opposite from the motor bracket 62. The heat conductiveplate 73 functions as a heat sink, and mounted on a portion of this heatsink that bends backward and alongside one of the castor legs 57 is aset of five heat evolving semi-conductor elements 74 which are utilizedin the control of the motor 63. Mounted across the front face ofthe heatsink 73 is a heat evolving resistor 75, which also is utilized in thecontrol of the motor 63. By attaching the heat sink 73 to the castor 56the necessary power dissipation, as represented by heat, can be achievedat a point on the wheelchair which is remote from the user, so thatthere is no exposure to a person in the chair. Wiring connecting to theelements 74 and resistor 75 have been omitted from the drawings, sincetheir exact location is not a part of the invention.

A lightweight cover is provided for the mobile power unit 53 whichshrouds the motor 63, the heat sink plate 73, the first speed reductionunit comprising the toothed gear wheel 64 and the large diameterreduction gear wheel 66, and the second reduction unit comprising thepinion gear 68 and the large diameter gear 61. This protective cover forthe power unit is shown in FIGS. 1 and 2, and is identified by thedesignating reference numeral 76. It is attached to a pair of brackets77, shown in FIGS. 12, 13 and 14 which depend from the axle for thedrive wheel 60, and is also fastened in place by attachment screws 90,seen in FIG. 1, which enter the top web 58 of the castor 56.

THE STEERING COLUMN Referring now to FIGS. 1 and 2, the tubular shaft 52rises vertically upward from the bearing housing 51 and passes through asupport bearing 78 inthe frame member 36 of the cantilevered left sideframework 35. The upper end of the tubular shaft 52 turns rearwardlytoward the left side arm rest 5 to present a tiller arm 79,

' and mounted on the upper, rear end ofthe tiller arm 79 is arectangular control box 80.

The control box 80 is shown on an enlarged scale in FIGS. 9, 10 and 11.It has aremovable cover 81 which mounts a vertical steering handle 82.The handle 82 is hollow and extending through the handle 82 is avertically depressible speed selector rod 83. The rod 83 is biasedupward by a spring 84 to the position shown in FIG. 9. Within thecontrol box 80 is a set of three speed selector switches 85 which aretiered one above the other with their operating heads 91 extending intothe path of travel of the speed selector rod 83. As is readily apparentfrom FIG. 9, the speed selector rod 83 may be depressed to successivelymove its lower end against the operating heads of the switches 85.

A forward reverse switch 86 is mounted within the control box 80. Also,a mechanism is provided which may cut out use of the lowermost of thespeed selector switches 85. This mechanism is a bracket 87 that has atip 88 which can be moved into the vertical path of travel of the bottomend of the speed selector rod 83. The bracket 87 is pivotally mounted,and has a small finger 89 at its upper end which can be operated uponremoval of the cover 81, as indicated in FIG. 11, so that the bracket 87may either be put into operative position, or swung aside to have noaffect. By swinging the tip 88 into the operative position of blockingfull downward movement of the rod 83, the downward motion of the speedselector rod 83 is arrested before it comes to the last speed selectorswitch 85. Thus, if the lowermost speed selector switch 85 is a highspeed switch the mechanism can be adjusted so that the user of thewheelchair cannot bring the chair into a high speed condition. Controlwires 55 from the speed selector switches 85 and the forward reverseswitch 86 pass into the top of tubular shaft 52 and extend down to thepower unit 53, as was previously identified in the description for FIG.12. The cover 81 can be removed by loosening a screw 92, shown in FIG.10, so that when in the palm and fingers of most all persons, and thegripping type muscular action is such that normal people will readilyassociate the gripping action with the turning of the tiller arm, sothat steering can be safely carried out by elderly people, invalids andother infirm individuals. The speed selection which is provided by thedepressible rod 83 calls for a distinctly different muscular action thanfor the steering accomplished by gripping the handle 82 in ones palm andfingers. A thumb motion is required for depressing the speed selectorrod 83, and a motion of a thumb is a human motor action quite separateand distinct from palm movements. Thus, it is believed that twodistinctly different muscular coordination systems are brought into playin the operation of the chair, which lessens operator confusion ascontrasted with steering and speed controls which simultaneously use apalm for steering and speed selection.

The tubular shaft 52 together with the power unit 53 at the lower endand the tiller arm 70 and control box 80 at the upper end forms asteering column which rests upon the ground at all times, exceptpossibly in extreme conditions of uneven terrain that are abnormal towheelchair use. Sharp turns for high mobility can be made by easymovements of the tiller arm 79. It is usually desirable to place somelimit upon the degree of permissible rotation, so that reverse motion isnot unexpectedly encountered by wide swings of the arm 79. For thislimitation, an upright, stationary stop pin 93 is secured to the side ofthe bearing housing 51, as shown in FIGS. 8 and 13. A pair of radialextending fingers 94 are disposed on a collar 95 (see FIG. 8) whichrotates with the shaft 52. These fingers 94 will strike the stop pin 93to limit rotation of the steering column.

CONCLUSION The wheelchair of the invention provides an apparatusembodying several features, as have been discussed herein. Unique towheelchair construction is four wheel support in which a single groundengaging driving wheel is held against the terrain to maintain controlof the chair. The two rear wheels are on a pivoted axis, which providesa simulated point of engagement with a ground at the place of axlepivot, thus keeping all wheels on the ground. The two front wheels andthe simulated point of engagement of the rear wheels at the pivot of therear axle provides an effective tripodal support for the chair, with thecenter area of the chair, the battery mass, and an occupant all wellwithin the triangular outline of the tripod. One of the front wheels cannow be an effective drive wheel, and special supports for this drivewheel are eliminated. A unique braking mechanism for the pivoted rearwheels augments the construction through introduction of a lost motionconnection between wheel engaging brake shoes and the manually operableparts of the brake system. Further, the invention provides a steeringcolumn with a self contained power unit which is easily manipulated forboth steering and speed control.

I claim:

1. In a wheelchair having a chair, a set of ground engaging wheels andspace for an energy cell beneath the chair, the combination comprising:

a. a pivot located beneath and at the rear of the chair providing aturning axis along the longitudinal center of the wheelchair;

b. a rear axle connected substantially at its mid-point to said pivotfor tilting in a vertical, transverse plane;

c. a pair of ground engaging rear wheels, one at each end of said axle,located beneath the rear sides of the chair;

d. a pair of motion limiting abutments, one on each side of said pivot,that are each disposed in vertical alignment with said rear axle, and ata spaced distance therefrom when said rear axle is in the horizontal;

e. a front ground engaging idler wheel pivotally mounted at the frontand one side of the chair for turning movement about a vertical axis;

f. a drive motor unit pivotally mounted at the front of the chair on theside opposite said idler wheel, and having a drive motor and a dependingground engaging traction wheel in driven relation to the motor;

g. said ground engaging traction wheel, idler wheel and pivoted rearwheels forming tripodal support points for the chair with the centerarea of the chair encompassed within the triangle defined by saidtraction wheel, said idler wheel and said pivot; and

h. a steering shaft rising upwardly from said drive motor unit that ispivotable about a vertical axis for turning said drive motor unit.

2. A wheelchair as in claim 1 in which the chair has four legs dependingat the front and rear corners and there is i. a pair of longitudinaljoists one at each side and each extending between the bottoms of thechair legs at its side;

j. a pair of transverse joists, one extending between the front chairlegs and the other between the rear chair legs;

k. a pair of parallel, longitudinally extending rack rails set inboardfrom said longitudinal joists and extending between said transversejoists; and in which l. said rear axle passes beneath said rack rails,with the underside of the rack rails forming said motion limitingabutments; and in which m. said ground engaging rear wheels arepositioned inboard of said longitudinal joists and outboard of said rackrails.

3. A wheelchair as in claim 1 having:

i. a brake shaft extending between said ground engaging rear wheelspivotally supported from said rear axle;

j. brake surfaces on said brake shaft located adjacent said rear wheels;

k. and a brake lever cooperatively engaged with said brake shaft topivot the same and move said brake surfaces against said rear wheelsupon movement of the brake lever.

4. A wheelchair as in claim 1 in which said steering shaft extendsupward from the drive motor unit and turns rearward to form a turningtiller, and at its upper end mounts a control box with a substantiallyvertical,

l 1 palm grippable handle, and fromthe top of which there extends asubstantially vertically movable thumb de pressible speed controlmember.

5. A wheelchair as in claim 1 having:

i. a pair of cantilevered front wheel supporting frames each juttingforward of said chair at a side thereof;

j. a pair of brearing brackets each detachably mounted on one of saidframes with mounting means providing for reversing the positions of thetwo bearing brackets;

k. one of said bearing brackets mounting said ground engaging idlerwheel and the other of said bearing brackets mounting said groundengaging traction wheel.

6. A wheelchair as in claim 5, with a foot support depending from eachcantilevered front wheel supporting frames.

7. In a wheelchair having a chair, framework for the chair, and groundengaging wheels, the combination comprising:

a. a pivotally mounted axle mounted on the framework that tilts about anaxis transverse to the axle;

b. rotatable wheels at the ends of the axle;

c. a pair of links extending transversely from the axle which arepivotally attached to the axle at points spaced from the center ofrotation of said wheels;

d. a brake shaft extending between the wheels and joined to the ends ofsaid pair of links at points remote from their pivotal attachment to theaxle;

e. brake surfaces on the brake shaft disposed infacing relation to saidwheels;

f. a brake lever in a connection with said brake shaft permitting tiltof said shaft with respect to said lever, said brake lever movable totranslate said brake shaft and thereby pivot the shaft and said linksabout the pivotal attachment of the links to the axle to move said brakesurfaces toward and away from said wheels; and

g. means for operating said brake lever.

8. A wheelchair brake mechanism as in claim 7, wherein said connectionbetween the brake shaft and brake lever comprises a hook extending fromthe brake lever in which the brake shaft is held, such hook being inalignment with the axis of pivot of said axle.

9. In a wheelchair having a chair and a set of ground engaging wheelsthe supporting undercarriage for the chair comprising:

a. a set of four chair legs at the forward and rear corners of thechair;

b. a pair of longitudinal joists one at each side and each extendingbetween the bottoms of the chair legs at its side;

c. a pair of transverse joists, one extending between the front chairlegs and the other between the rear chair legs;

d. a pair of parallel, longitudinally extending rack rails set inboardfrom said longitudinal joists and extending between said transversejoists; and in which e. a pivot supported from the foregoing membershaving an axis of pivot on the longitudinal center line of thewheelchair;

f. an axle supported at its mid-point by said pivot and passing beneathsaid rack rails at a distance therebeneath permitting limited rocking ofthe axle about said pivot;

g. a pair of ground engaging rear wheels on said axle that are eachlocated between a longitudinal joist and a rack rail;

h. front wheel supporting frames extending forward from the front chairlegs; and

i. front ground engaging wheels mounted on said front wheel supportingframes.

10. In a wheel chair having a chair, framework for the chair, and groundengaging wheels, the combination comprising:

a. a pivotally mounted axle mounted on the framework that tilts about anaxis transverse to the axle;

b. rotatable wheels at the ends of the axle;

c. a brake member connected to said axle that pivots therewith tomaintain alignment between the brake member and axle;

d. braking surfaces on said brake member adjacent said wheels forbraking engagement therewith; and

e. a brake operating lever having a lost motion connection with saidbrake member, such lost motion being in the direction of tilt of thebrake member.

1. In a wheelchair having a chair, a set of ground engaging wheels andspace for an energy cell beneath the chair, the combination comprising:a. a pivot located beneath and at the rear of the chair providing aturning axis along the longitudinal center of the wheelchair; b. a rearaxle connected substantially at its mid-point to said pivot for tiltingin a vertical, transverse plane; c. a pair of ground engaging rearwheels, one at each end of said axle, located beneath the rear sides ofthe chair; d. a pair of motion limiting abutments, one on each side ofsaid pivot, that are each disposed in vertical alignment with said rearaxle, and at a spaced distance therefrom when said rear axle is in thehorizontal; e. a front ground engaging idler wheel pivotally mounted atthe front and one side of the chair for turning movement about avertical axis; f. a drive motor unit pivotally mounted at the front ofthe chair on the side opposite said idler wheel, and having a drivemotor and a depending ground engaging traction wheel in driven relationto the motor; g. said ground engaging traction wheel, idler wheel andpivoted rear wheels forming tripodal support points for the chair withthe center area of the chair encompassed within the triangle defined bysaid traction wheel, said idler wheel and said pivot; and h. a steeringshaft rising upwardly from said drive motor unit that is pivotable abouta vertical axis for turning said drive motor unit.
 2. A wheelchair as inclaim 1 in which the chair has four legs depending at the front and rearcorners and there is i. a pair of longitudinal joists one at each sideand each extending between the bottoms of the chair legs at its side; j.a pair of transverse joists, one extending between the front chair legsand the other between the rear chair legs; k. a pair of parallel,longitudinally extending rack rails set inboard from said longitudinaljoists and extending between said transverse joists; and in which l.said rear axle passes beneath said rack rails, with the underside of therack rails forming said motion limiting abutments; and in which m. saidground engaging rear wheels are positioned inboard of said longitudinaljoists and outboard of said rack rails.
 3. A wheelchair as in claim 1having: i. a brake shaft extending between said ground engaging rearwheels pivotally supported from said rear axle; j. brake surfaces onsaid brake shaft located adjacent said rear wheels; k. and a brake levercooperatively engaged with said brake shaft to pivot the same and movesaid brake surfaces against said rear wheels upon movement of the brakelever.
 4. A wheelchair as in claim 1 in which said steering shaftextends upward from the drive motor unit and turns rearward to form aturning tiller, and at its upper end mounts a control box with asubstantially vertical, palm grippable handle, and from the top of whichthere extends a substantially vertically movable thumb depressible speedcontrol member.
 5. A wheelchair as in claim 1 having: i. a pair ofcantilevered front wheel supporting frames each jutting forward of saidchair at a side thereof; j. a pair of brearing brackets each detachablymounted on one of said frames with mounting means providing forreversing the positions of the two bearing brackets; k. one of saidbearing brackets mounting said ground engaging idler wheel and the otherof said bearing brackets mounting said ground engaging traction wheel.6. A wheelchair as in claim 5, with a foot support depending from eachcantilevered front wheel supporting frames.
 7. In a wheelchair having achair, framework for the chair, and ground engaging wheels, thecombination comprising: a. a pivotally mounted axle mounted on theframework that tilts about an axis transverse to the axle; b. rotatablewheels at the ends of the axle; c. a pair of Links extendingtransversely from the axle which are pivotally attached to the axle atpoints spaced from the center of rotation of said wheels; d. a brakeshaft extending between the wheels and joined to the ends of said pairof links at points remote from their pivotal attachment to the axle; e.brake surfaces on the brake shaft disposed in facing relation to saidwheels; f. a brake lever in a connection with said brake shaftpermitting tilt of said shaft with respect to said lever, said brakelever movable to translate said brake shaft and thereby pivot the shaftand said links about the pivotal attachment of the links to the axle tomove said brake surfaces toward and away from said wheels; and g. meansfor operating said brake lever.
 8. A wheelchair brake mechanism as inclaim 7, wherein said connection between the brake shaft and brake levercomprises a hook extending from the brake lever in which the brake shaftis held, such hook being in alignment with the axis of pivot of saidaxle.
 9. In a wheelchair having a chair and a set of ground engagingwheels the supporting undercarriage for the chair comprising: a. a setof four chair legs at the forward and rear corners of the chair; b. apair of longitudinal joists one at each side and each extending betweenthe bottoms of the chair legs at its side; c. a pair of transversejoists, one extending between the front chair legs and the other betweenthe rear chair legs; d. a pair of parallel, longitudinally extendingrack rails set inboard from said longitudinal joists and extendingbetween said transverse joists; and in which e. a pivot supported fromthe foregoing members having an axis of pivot on the longitudinal centerline of the wheelchair; f. an axle supported at its mid-point by saidpivot and passing beneath said rack rails at a distance therebeneathpermitting limited rocking of the axle about said pivot; g. a pair ofground engaging rear wheels on said axle that are each located between alongitudinal joist and a rack rail; h. front wheel supporting framesextending forward from the front chair legs; and i. front groundengaging wheels mounted on said front wheel supporting frames.
 10. In awheel chair having a chair, framework for the chair, and ground engagingwheels, the combination comprising: a. a pivotally mounted axle mountedon the framework that tilts about an axis transverse to the axle; b.rotatable wheels at the ends of the axle; c. a brake member connected tosaid axle that pivots therewith to maintain alignment between the brakemember and axle; d. braking surfaces on said brake member adjacent saidwheels for braking engagement therewith; and e. a brake operating leverhaving a lost motion connection with said brake member, such lost motionbeing in the direction of tilt of the brake member.